Group thrust compensator



y 5, 1966 l G. s. BlSHOP ET AL 3,258,914

GROUP THRUST COMPENSATOR Filed Dec. 26, 1965 5 Sheets-Sheet 1 GEOFFREYs. isnaP INVENTORS RONALD w. How/4RD BY} A TTOR/VEVS y 5, 1956 a. s.BISHOP ET AL 3,258,914

GROUP THRUST GOMPENSATOR 5 Sheets-Sheet 2 Filed Dec. 26, 1963 @EOFFREY 8)SM P INVENTORS ATTORNEYS July 5, 1966 s. BISHOP ET AL 3,

GROUP THRUST COMPENSATOR Filed Dec. 26, 1965 5 Sheets-Sheet -3 t 110 100j 76 I ll! 1| 103 25 551% r K 111 INVENTORS GEOFFREY s. BisHoP RauALo wHOVARD U Q as A TTORNEYs United States Patent 3,258,914 GROUP THRUSTCOMPENSATOR Geoifrey Stanley Bishop, Luton, and Ronald Walter Howard,Gravesend, England, assignors to Elliott Brothers (London) Limited,London, England, a British company Filed Dec. 26, 1963, Ser. No. 333,473Claims priority, application Great Britain, Jan. 4, 1963, 533/63 6Claims. (Cl. 6035.6)

This invention relates to a group thrust compensator for an aircraftengine installation, that is to say, a device which ensures that a groupof jet engines is always delivering a predetermined total thrust.

In VTOL aircraft employing a plurality of lift engines, possiblyarranged in groups contained in wing pods, and possibly operating inconjunction with a further one or more engines delivering both a liftthrust and a forward thrust, it is of supreme importance that the liftthrust should be maintained at a predetermined level since a suddenvariation, be it upwards or downwards, in the lift may have disastrouseffects before the human pilot can correct it.

The object of the present invention is to provide a simple controlarrangement which functions automatically to maintain a predeterminedthrust, even when there is a tendency to large variations, such as willresult from the failure of one engine of the group.

The invention consists of a group thrust compensator for a group of jetengines generating a lift thrust comprising a double-acting fluidcylinder and a piston and piston rod contained therein for each engineof the group, a source of fluid pressure for each engine to provide afluid pressure corresponding to the thrust delivered by the engine whenin operation, means to apply the fluid pressure from each source to theend of the respective cylinder containing the piston rod, a connectionfrom the source of fluid pressure on each engine to a common chamberthrough a non-return valve, a connection from the common chamber to theother end of each cylinder, a calibrated leak device to allow the fluidin the common chamber to escape at a controlled rate, mechanicalconnections from the piston rods of all the cylinders to a single enginethrottle control controlling the throttles of all the engines in thegroup, and resilient means acting on the pistons against the pressurefrom the common chamber, whereby all the pistons are acted upon at theone side by the highest pressure derived from the plurality of sources,each piston is acted upon at its other side by a pressure derived fromthe source on the associated engine, and the movements of all thepistons are transmitted to the throttle control.

There may be a further cylinder or cylinders containing pistons andpiston rods, each further cylinder being connected at the end containingthe piston rod by pressure from a source associated with an enginedelivering a combined lift and forward thrust, the pressure source inthis case having no connection to the common chamber, the piston rod ofeach further cylinder being mechanically connected to the throttlecontrol. The further cylinder or cylinders may be of different diameterfrom that of the cylinders associated with the engines of the group.

Two embodiments of the invention Will now be described with reference tothe drawings accompanying this specification, in which:

FIGURE 1 is a diagrammatic cross section of one form of group thrustcompensator according to the invention;

FIGURE 2 diagrammatically shows in ghosted form an arrangement of agroup of three lift engines in a wing pod, a fourth combined lift-thrustengine in a separate pod and the interconnections between the groupthrust 3,258,914 Patented July 5, 1966 compensator, the group enginethrottles and the pilots controls;

FIGURE 3 is a diagrammatic section of another group thrust compensatoraccording to the invention; and

FIGURE 4 is a cross section showing a detail of the group thrustcompensator of FIGURE 3.

FIG. 5 is a cross-section showing a detail of an autoselector valve ofFIG. 4.

Referring initially to FIGURE 1, a group thrust compensator according tothe invention comprises a casing 11 which contains four fluid cylinders,respectively 12, 13, 14 and 15. Each fluid cylinder contains a piston,re-

spectively 16, 17, 18 and 19. The piston 16 is provided with a pistonrod or ram 20 which passes through the one end 21 of the cylinder 12,and in a similar manner the piston 17 has a piston rod 22 passingthrough the end 23 of the cylinder 13, the piston 18 has a piston rod 24passing through an end 25 of the cylinder 14 and the piston 19 has apiston rod 26 passing through the end 27 of the cylinder 15. The otherends of the cylinders 12, 13, 14 and 15 are open to a chamber 28 formedby one end of the casing 11. Stops 29 are provided to prevent thepistons 16, 17, 18 and 19 moving out of their respective cylinders underthe influence of fluid pressure and of a spring 30, supported by anabutment 31, which acts upon all the piston rods through the medium of acommon member 32.

At this stage, it is desirable to consider the arrangement of the groupthrust compensator in relation to the engines and controls of theaircraft, which is shown in the diagram of FIGURE 2. FIGURE 2 is aghosted diagram showing an aircraft having a fuselage 33, wing 34, tailplane 35 having control surfaces 36 and a rudder 37 having controlsurfaces 38. Wing flaps providing control surfaces for braking purposesare indicated at 39. Three lift engines, respectively 40, 41 and 42, arelocated in a wing pod 43 while a combined lift/thrust engine 44 islocated in a wing pod 45. The group thrust compensator 46 is locatedclose to the group of lift engines 40, 41, 42 inside the wing pod 43.Each of the lift engines 40, 41 and 42 is provided with a source whichproduces a fluid pressure depending upon the pressure in the respectivejet pipe and therefore corresponding to the thrust output of the engine.This may consist of a Pitot tube in the jet, or a static tapping, or itmight consist of two identical venturis, one having its inlet closed,the difference in pressure in the two venturis being a measure of thethrust pressure in the jet.

The fluid pressure from the source associated with the engine 40 istransmited to the group thrust compensator through a pipe 47, thepressure from the source associated with the engine 41 is transmitted tothe group thrust compensator through a pipe 48, and pressure from thesource associated with the engine 42 is transmitted to the group thrustcompensator through a pipe 49. A simisimilar source of fluid pressure isprovided for the engine 44 and the pressure is transmitted by a fourthpipe 50 to the group thrust compensator 46.

Reverting now to FIGURE 1, the three pipes 47, 48 and 49 are shownconnected respectively to the closed ends of the cylinders 12, 13 and14. The pipe 47 is provided with a branch 51 which is connected througha non-return valve 52 to the common chamber 28 and in similar fashionthe pipe 48 is provided with a branch 53 connected through a non-returnvalve 54 to the chamber 28, and the pipe 49 is provided with a branch 55connected through a non-return valve 56 to the chamber 28, the valvesall being arranged in such a sense that fluid under pressure may passinto the chamber 28 but not out of it. The chamber 28 is also providedwith a leak device 57 through which fluid under pressure in the chamber28 may leak at a controlled rate into an exhaust pipe 58.

The three cylinders 12, 13 and 14 are of identical diameter but it willbe observed that the cylinder 15 is of smaller diameter and is longer,so that the piston 19 may have a longer stroke. The pipe from thecombined lift/thrust engine 44 is connected to this cylinder but thereis no branch from the pipe 50 connected to the chamber 28.

The common member 32 shown in FIGURE 1 is mechanically connected to arod 59 which forms the throttle control run and is mechanicallyconnected to the three engines 40, 41 and 42 by means of linkage whichis also connected to the pilots primary throttle control 61 (FIGURE 2-).

In operation, and assuming that all the engines are running normally, afluid pressure corresponding to the thrust output of each of the engines40, 41 and 42 is applied respectively to the cylinders 12, 13 and 14,while a pressure corresponding to the output of the engine 44 is appliedto the cylinder 15. By virtue of the non-return valves 52, 54 and 56 thepressure in the chamber 28 is equal to the highest of the threepressures in the pipes 47, 48 and 49. l

A study of one of the cylinders will show that the pressure in thechamber 28 acts upon the outer face of the piston and this pressure is,as previously explained, the highest pressure existing in any of thejets. The other face of the piston is acted upon only by the jetpressure in the associated engine and, because of the presence of thepiston rod or ram this face has a smaller effective area, so that innormal conditions the piston would move to the right in FIGURE 1.However, such movement is resisted by the spring 30 which applies suchforce as to make up for the difference in the forces acting on the twosides of the three pistons 16, 17 and 18. If the three jet pipepressures of the three engines are equal then the pressures in the threecylinders 12, 13 and 14 and in the chamber 28 are all equal and thespring 30 applies equal mechanical pressure to the piston rods 20, 22and 24, to balance the differences in the forces acting on the two facesof the respective pistons. If, now, one of the engines 40, 41 or 42should develop a reduced output, or fail, then the fluid pressure actingon the inner face of the respective piston will fail, whereas thepressure in the chamber 28 will be unaffected because of the presence ofthe non-return valves 52, 54 and 56. In consequence the force acting onthe inner face of the piston associated with the faulty engine eitherdrops in magnitude or disappears altogether. As a result the forces onthe pistons become unbalanced and they all move together to the right inFIGURE 1, thereby compressing the spring 30 until a new balancedposition is reached. This movement of the common member 32 causes anequal movement of the rod 59 and it is arranged that the direction ofmovement of the rod 59 is such as to open the throttles of all theengines so as to restore the total thrust of the engines to its originallevel.

It will be observed that while the engine 44 communicates a pressure toits cylinder 15 corresponding to its jet pipe pressure it can have noeffect on the pressure in the chamber 28, but the pressure in thecylinder 15 does add to the total force acting to assist the spring 30,so that a loss of thrust in the engine 44 will also cause the throttlesof all the engines to be opened. Due to the fact that the cylinder 15has a smaller cross-sectional area, a given loss in jet pressure willhave less effect than the same loss of pressure in the three liftengines. However, this is what is required, since a part of the outputof the engine 44 is used for providing a forward thrust and only a partis used for lifting.

The spring 30 may be a biasing spring, as shown, acting through thecommon member 32. However, separate springs can be provided, and a knowntype of adding mechanism may be used in place of the common member 32,as shown diagrammatically in FIGURE 3, in which it will be seen that thepiston rods 20, 22, 24 and 26 are provided with abutment plates andseparate springs, respectively 62, 63, 64. and 65 each hearing at itsother end on a fixed abutment plate. The four piston rods are coupledtogether through an adding mechanism, the piston rods 20 and 22 beingpivoted to the ends of a bar 66 the centre of which is pivoted to a rod67, and the piston rods 24 and 26 being pivoted to the ends of a bar 68the centre of which is pivoted to a rod 69, While the rods 67 and 69 arepivoted to the ends of a bar 70 the centre of which is coupled by a rod71 to one end of a bar 72 which receives the mechanical outputrepresenting the algebraic sum of the movements of the four piston rods.The other end of the bar 72 is coupled to a rod 73, equivalent to therod 59, while the centre of the bar 72 is coupled through a rod 74 tothe pilots primary control.

The lift/thrust engine 44 is provided with a separate throttle controlwhich is not shown in the figures.

FIGURE 4 shows a modification of the arrangement depicted in FIGURE 1.In this case the casing 11 containing the integral cylinders 12, 13, 14and 15 and the chamber 28 are replaced by four separate cylinders,respectively 75, 76, 77 and 78, and a separate container 79. Thecylinder 75 is fed through a pair of pipes, respectively 80 and 81, thecylinder 76 is fed by a pair of pipes 82 and 83, the cylinder 77 is fedby a pair of pipes 84 and 85, and the cylinder 78 is fed by a pair ofpipes 86 and 87. In each case the two pipes of the pair are connected tothe one source at the engine and at the other end to an autoselectorvalve, respectively 88, 89, 90 and 91. The autoselector valve is shownin section in FIGURE 5 and comprises a casing 92 having a bore 93 whichcontains a valve member 94. The cylinder 93 has inlets at opposite endswhich are connected to the two pipes of a pair, for example, pipes 80and S1, and the cylinder 93 has outlet ports, respectively and 96 spacedsome distance from its ends. Both the pipes 30 and 81 carry a fluidpressure from the respective pressure source provided on the associatedengine and in normal operation the valve member 94 occupies the centreposition, as shown. If, however, one of the pipes 80 or 81 shouldfracture, the pressure acting on one end of the valve member 94 willfall and the valve will move to one end or the other of the cylinder 93and thereby close the port 95 or 96 associated with the inlet connectedto the fractured pipe. This is one example of the way in whichredundancy may be employed in connection with the invention.

Reverting to FIGURE 4, since the cylinders 75, 76, 77 and 78 are now fedthrough pairs of pipes the taking of a branch connection from one pipeof a pair to feed the container '79 is not advisable, unless it isdesired to provide redundant branch pipes, in which case it would benecessary to employ further autoselector valves and use two branchpipes. However, FIGURE 4 shows a pipe 97 leading from the one end ofcylinder 75 to a nonreturn valve 98, which is exactly the same as thenonreturn valves 52, 54 and 56 in FIGURE 1. In the same way, a pipe 99leads from the one end of the cylinder 76 through a non-return valve 100to the container 79 and the cylinder 77 is similarly connected through apipe 101 and a non-return valve 102. The other ends of the respectivecylinders 75, 76, 77 and 78 are connected by means of pipes,respectively 113, 114, 115 and 116, to the container 79. A controlledleak device 103 and an exhaust pipe 105 are connected to the container79 and fulfill exactly the same functions as the member 57 and pipe 58in FIGURE 1. The four piston rods 106, 107, 108 and 109 bear upon acommon member 110, equivalent to the member 32 and this is engaged witha spring 111 and with a rod 112, equivalent to the members 30 and 59respectively in FIGURE 1.

The arrangement of FIGURE 4 functions in precisely the same way as thatof FIGURE 1. The container 79 is maintained at a fluid pressurecorresponding to that of the highest pressure in any of the three pairsof pipes and the said other end of each of the four cylinders issubjected to this pressure, While the said one end of each cylinder isfed only with the pressure derived from the respective jet pipe, whilethe spring 111 provides an extra force to balance the total forcesacting on the two faces of each of the four pistons. If any one of thefour engines should suffer a reduction in thrust output, therebyreducing the pressure in the associated jet pipe, then the force actingon the one or rearward face of the respective piston is reduced, so thatthe pressure in the container 79 is enabled to move all four pistons ina direction to the right in FIGURE 4 and thereby move the rod 112connected to the throttle control to open all the engine throttles.

Various modifications may be made in the described embodiments withinthe scope of the invention. For example, a mechanism equivalent to azero rate spring, sometimes called a bang-bang mechanism, may besubstituted for the springs 30, 6266 and 111. Alternatively a pneumaticsystem may be used. In either case the important feature of theinvention, that the information on Which the control operates is allobtained directly from the engines and no external source is required.

It will be understood that embodiments other than those described andillustrated, or modifications thereof, may be devised within the scopeof the invention as defined in the appended claims.

We claim:

1. A group thrust compensator for a group of jet engines generating alift thrust comprising a double-acting fluid cylinder and a piston andpiston rod contained therein for each engine of the group, a source offluid pressure for each engine to provide a fluid pressure correspondingto the thrust delivered by the engine when in operation, means to applythe fluid pressure from each source to the end of the respectivecylinder containing the piston rod, a connection from the source offluid pressure on each engine to a common chamber through a non-returnvalve, a connection from said common chamber to the other end of eachcylinder, a calibrated leak device to allow fluid in the common chamberto escape at a controlled rate, mechanical connections from the pistonrods of all the cylinders to a single engine throttle controlcontrolling the throttles of all the engines in the group, and resilientmeans acting on the pistons against the pressure from said commonchamber, whereby all the pistons are acted upon at the one side by thehighest pressure derived from the plurality of sources, each piston isacted upon at its other side by a pressure derived from the source onthe associated engine, and the movements of all the pistons aretransmitted to the throttle control.

2. A compensator as claimed in claim 1 comprising a further cylinder orcylinders containing pistons and piston rods, each further cylinderbeing connected at the end containing the piston rod to pressure from asource associated with an engine delivering a combined lift and forwardthrust, the pressure source in this case having no connection to thecommon chamber, the piston rod of each further cylinder beingmechanically connected to the said throttle control, each combined liftand thrust engine having a throttle control which is separate from thesaid throttle control.

3. A compensator as claimed in claim 2 in which each further cylinder isof diiferent diameter to that of the cylinders associated with theengines of said group.

4. A compensator as claimed in claim 1 in which all said piston rods arerigidly connected to a member coupled to said engine throttle control,said resilient means comprising a single spring which, during normaloperation, compensates for the difference in the forces acting on thetwo sides of each piston due to the difference in eifective arearesulting from the presence of said piston rod.

5. A compensator as claimed in claim 1 in which all said piston rodsmove independently, each being provided with a spring, comprising anadding mechanism coupled to all said piston rods and to said throttlecontrol 'by which the algebraic sum of the individual piston positionsis transmitted to said throttle control.

6. A compensator as claimed in claim 1 comprising a pair of pipes fromeach source of fluid pressure, an autoselector valve for each pair ofpipes to cut off the connection with either pipe if the pressure thereinshould fail, each autoselector valve being connected to that end of onecylinder containing the piston rod, and a connection from the said endof each cylinder to the common chamber through the said non-returnvalve.

References Cited by the Examiner UNITED STATES PATENTS 2,737,015 3/1956Wright 35.6 3,159,000 12/1964 McCombs 60-3915 3,176,936 4/1965 Howard etal. 6039.15 X

MARK NEWMAN, Primary Examiner.

D. H RT, Assistant Examiner.

1. A GROUP THRUST COMPENSATOR FOR A GROUP OF JET ENGINES GENERATING ALIFT THRUST COMPRISING A DOUBLE-ACTING FLUID CYLINDER AND A PISTON ANDPISTON ROD CONTAINED THEREIN FOR EACH ENGINE OF THE GROUP, A SOURCE OFFLUID PRESSURE FOR EACH ENGINE TO PROVIDE A FLUID PRESSURE CORRESPONDINGTO THE THRUST DELIVERED BY THE ENGINE WHEN IN OPERATION, MEANS TO SUPPLYTHE FLUID PRESSURE FROM EACH SOURCE TO THE END OF THE RESPECTIVECYLINDER CONTAINING THE PISTON ROD, A CONNECTION FROM THE SOURCE OFFLUID PRESSURE ON EACH ENGINE TO A COMMON CHAMBER THROUGH A NON-RETURNVALVE, A CONNECTION FROM SAID COMMON CHAMBER TO THE OTHER END OF SAIDCYLINDER, A CALIBRATED LEAK DEVICE TO ALLOW FLUID IN THE COMMON CHAMBERTO ESCAPE AT A CONTROLLED RATE, MECHANICAL CONNECTIONS FROM THE PISTONRODS OF ALL OF THE CYLINDERS TO A SINGLE ENGINE THROTTLE CONTROLCONTROLLING THE THROTTLES OF ALL THE ENGINES IN THE